The present invention is directed to a circuit and method of controlling the gain of an audio amplifier via a microprocessor. It is known to use a p-channel or n-channel junction field effect transistor (FET) for controlling the gain of a circuit. Such prior art FET-controlled circuits depend on the particular parameters of the particular FET used, such as the pinch-off voltage, the minimum resistance of the FET, R.sub.DS (on), and the like. Thus, the particular gain achieved in the circuit varies with the particular FET used, and varies from one type of FET to another.
It is the object of the present invention to provide a constant and predictable gain of an amplifying circuit that is independent of the particular FET used, and the parameters thereof. The present invention has special application to an audio-amplifying circuit, although other fields are also within the domain of the present invention.